Preparation And Mechanical Properties Of SiC Reinforced ZL101 Composites By Semi-solid Thixoforging

ZL101 is a typical aluminum-silicon alloy suitable for semi-solid processing.It belongs to the cast aluminum alloy with relatively simple composition,lower cost,better casting fluidity and wider semi-solid range,The particle-reinforced aluminum-based composite material combines the toughness and specific strength of the base metal,the strength,hardness and wear resistance of the particles by adding a particle-reinforcing phase in the metal matrix,which is a comprehensive performance.Excellent materials can meet the higher requirements for materials put forward by the development of modern technology.Semi-solid technology has the advantages of short process,low thermal cracking tendency,and good forming.In this paper,combining the preparation method of particle-reinforced aluminum-based composite material and the thixoforming process,the micron-sized particle-reinforced aluminum-based composite material is successfully prepared,and the composite The heat treatment process of the material has studied the influence of different conditions on the structure and mechanical properties of the composite material,so as to promote the wide use of the semi-solid thixotropic particle reinforced aluminum matrix composite material in the direction of structural parts.In this paper,the pretreatment process parameters of SiC particles are selected,and SiC particle prefabricated blocks are prepared,and then the reinforcement particles are uniformly added to the metal melt by the method of semi-solid mechanical stirring,and the semi-solid composites blanks are successfully prepared by the near liquidus method.The microstructure of the semi-solid billet is obvious equiaxed crystal grains.SEM and EDS analysis found that the SiC particles are well bonded to the matrix interface,and the eutectic Si phase and needle-like second phase surrounding the grain boundary are distributed in the middle of the crystal grains,and A small amount of Mg₂Si phase.The average grain size of the alloy without SiC particles is 60.18μm.After adding SiC reinforcement particles,the grain size has been significantly refined,and the degree of refinement is proportional to the amount of SiC particles added,when the SiC content is 4.2Vol.%At this time,the crystal grain size is the minimum 39.93μm.The micron-sized SiC particles are uniformly distributed in the matrix.When the SiC content is greater than 2.5Vol.%,more obvious agglomerations are found in the microstructure.The prepared composite material blank was subjected to secondary remelting heating and semi-solid thixoforming,and the different forming positions of the composite material after forming were studied and analyzed.The results show that there are big differences in the microstructure of different parts of the composite after thixoforming.The amount of grain deformation in the lateral plate structure is small,and the thixoforming process does not have a significant impact on the distribution of SiC particles.The grain size of alloys and composites has decreased significantly;in the bottom structure,the grains have been relatively small.With a large degree of deformation,the distribution of SiC particles has changed significantly,from a uniform distribution in the as-cast state to a band-like distribution along the flow direction.The average grain size of the base alloy and4.2Vol.%SiCp/ZL101 composite material becomes 37.74μm and 28.96μm,which are reduced by 37.29%and 27.47%,respectively;the hardness is 55.7HV and 74.9HV,respectively.After thixoforming,the tensile strength,yield strength and elongation of the base alloy lateral plate are 142.42MPa,80.68MPa and 9.91%;after adding the reinforcing particles,the tensile strength increases to a certain extent,among which the SiC content is 2.5Vol.%Compared with the alloy,the tensile strength,yield strength and elongation of the composite material have increased by 9.63%,3.71%and 10.9%respectively;the tensile strength and yield strength of the bottom of the composite material are slightly improved compared with that of the lateral plate,and the elongation and There is almost no change in hardness.The fracture surface showed the characteristics of quasi-cleavage fracture.The heat treatment process has a significant impact on the microstructure and mechanical properties of the composite material.T4 solution treatment caused the eutectic Si to spheroidize,and the average grain size of the composite material did not grow significantly.After T4 solution treatment,the tensile strength,yield strength and elongation of the base alloy lateral plate are 234.68MPa,126.31MPa and 7.52%,respectively,Compared with before solution treatment,the tensile strength and yield strength increased by 64.78%and 56.55%,while the elongation decreased by 24.12%.The bottom sample is 204.01MPa,145.24MPa and3.22%respectively.The strength of composite materials with different SiC contents has been significantly improved.After T6 treatment,the mechanical properties of the bottom have a greater increase than that of the lateral plate;among them,the mechanical properties of the 2.5Vol.%SiCp/ZL101composites are the highest,and the tensile strength and yield strength of the lateral plate and bottom are 293.91MPa,232.2MPa and 328.65MPa,277.76MPa;Compared with the base alloy after T6 heat treatment,it has increased by 16.63%,18.92%,22.25%,19.49%,and the elongation has increased by 47.68%and 38.27%,respectively;the reinforcement particles have played a role in the comprehensive performance of the composite material.Good results.Heat treatment makes the composite material hardness up to 132.4HV.The fracture morphology of the matrix alloy presents the characteristics of cleavage fracture,which is an obvious brittle fracture.After adding 0.8Vol.%of SiC particles,the material turns into ductile-brittle mixed fracture,and the ductile fracture characteristics are more obvious;the fracture morphology of the composite material is similar to that of the composite material.The content of SiC particles is related,and the increase of SiC content reduces the number of dimples in the fracture of the composite material,and the area of cleavage increases,which tends to be brittle fracture.